But I also belong to a generation which knows, or thinks it knows, that of all life’s factors, body size is the one which lies most simply under one’s own control. Eat less, mainly plants, and move around more. That generally works.

"If you're the kind of person (for whom) it takes a lot of food to make you feel full, of course you're going to have a harder time controlling your food intake"

Prof Susan Jebb

Susan Jebb, Oxford professor of diet and population health and senior government adviser, takes a slightly different approach. She says that the prejudice against overweight people is “completely obstructive”, and evidence shows that the more you nag or mock fat people, the more they eat. She also accepts research suggesting that genetic inheritance accounts for 20 to 75 per cent of weight problems: some people are programmed to have a lot of appetite and store fat efficiently. Any old-fashioned farmer will tell you this is the case: some piglets are fondly described as “good doers”, others hard to fatten.

She also states the obvious, which is that easy access to high-calorie food on every street doesn’t make it any easier. As Victoria Wood put it, you can’t walk 20ft down any high street without fancying “a bucket of milky coffee and a muffin the size of a bowler hat”. The North of England – where statistics show most obesity – has an even bigger instant-grub problem than the South: I once counted 10 branches of Greggs in a 10-minute walk through Manchester, closing only when the evening chip-shops opened.

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Add to that the nationwide ready-meal culture where seemingly sensible dishes are loaded with fats and sugars to create tastiness; acknowledge the prevalence of work (or indeed unemployment) stress, and you have a nation yearning for something tasty. Add it all together and you have a perfect storm of weight gain. Or, as the British Medical Journal put it, with a shaky grip of appropriate metaphor, “a tsunami of obesity”.

Professor Jebb suggests that the wave of lipids is not due to a “national collapse in willpower”, but our changed environment. People do want to lose weight, she says, but they find it hard. Food addiction is hard to break: you can’t, as with alcohol or drugs, vow never to touch the stuff again. The trouble is, Professor Jebb also provides some convenient excuses for those keen to absolve themselves of personal responsibility.

People who mentor children with serious problems – physical, mental or social – know that it pays to encourage effort. They see the satisfaction that brings, and know that making constant excuses for a condition or circumstances creates a victim mentality and a sense of helplessness. Dieters know the moment you say it’s your “big bones” or genes, or unhappiness, you give up and reach for a doughnut because dammit, you’re worth it. Eating isn’t a crime. As the magnificent Vanessa Feltz said (before she took the gastric-band route): “I don’t smoke, I hardly drink, I’m a nice girl, I’m a good mum. I’m not having wild sex parties with strangers, so part of me feels entitled to have some trifle.”

Fatness is complicated for both sexes, but especially, I think, for women: several studies indicate that men are better at losing weight once they make their minds up because they are culturally less troubled by feelings of guilt and helplessness. My favourite diet book ever is Nigel Lawson’s, a sort of “Mr Toad Gets Fit”. It could be summarised thus: “There I was, a fine fellow and very important politician. Got too fat. Fell over skiing, couldn’t get up. Decided to diet. Told wife Therese to make me some diet sort of food. Ate it. Replaced claret with Diet Coke, an agreeable drink. Lost the weight. Was still a fine important fellow, only thinner. That’s it.”

Some query Lord Lawson’s choice of diet, but you can’t fault his brisk, unapologetic, motivated tone. It could be that a bit of arrogance is the most useful weight-loss tool of all.